<p> A change in fluvial style and a change in the stacking pattern of fluvial channel sandstone bodies occur across the Buckley&square;Fremouw formational contact in the central Transantarctic Mountains in Antarctica. Strata in the Buckley Formation are characterized by thick floodplain deposits in the Middle to Upper Permian Buckley Formation; whereas, stacked interconnected sandstone bodies occur in the Triassic Fremouw Formation (Barrett et al., 1986; Isbell &amp; Macdonald, 1991a, 1991b; Collinson et al., 1994; Isbell et al., 1997; 2005). Such changes in fluvial stacking patterns have been attributed to changes in the creation of accommodation within basins due to changes in relative sea level, changes in accommodation due to tectonism, and changes in sediment flux associated with loss of vegetation and increased erosion rates following the end-Permian mass extinction event. To explain the changes in the Buckley-Fremouw Formation in Antarctica, Isbell &amp; Macdonald (1991a, 1991b) and Isbell et al. (1997) argued for changing tectonic conditions in the basin while Retallack et al. (2006) suggested the changes were associated with the P&square;T mass extinction event causing the loss of peat forming plants. This study found that the change in the accommodation across the PTB was a result of tectonism based on evidence of changing sandstone composition, changing paleocurrent orientations, and changing fluvial stacking patterns between the Buckley Formation and the Fremouw Formation. This suggests differential subsidence in the Transantarctic foreland basin with an under-filled basin in the Late Permian changing to an over-filled basin in the Early Triassic. </p>

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<p> Late Jurassic through Early Cretaceous strata of the Gannett Group record initial development of the Sevier thrust belt and adjacent foreland basin. Concepts of nonmarine sequence stratigraphy were used to determine the depositional and base level history of the Gannett Group in southeastern Idaho and western Wyoming. Base level fluctuations were driven entirely by tectonic processes, while tectonic uplift in the source area was a major control on sequence development. Six measured sections were revisited or measured and correlated using the concepts of sequence stratigraphy. Four distinct sequences were identified and correlated. Each sequence can be divided into degradational, transitional, or aggradational systems tracts. Where the degradational systems tracts are preserved, they are represented by thin conglomerates. Transitional systems tracts overly the degradational systems tracts and consist of thick sections of laterally discontinuous sandstone and fluvial overbank muds, which grade laterally into continuous limestone and calcareous mudstones that comprise the aggradational systems tract.</p>

<p> The purpose of this study was to identify the geologic signature of paleostorm events within the mid-continent region. This research aimed to create a better understanding of the long-term geologic history of major storms and to allow for better-informed projections regarding future return periods for such storms. The study locations were Cheyenne Bottoms Wildlife Refuge, Kansas and Canton Lake, Oklahoma. To determine the geologic signature of major storms, sediment cores were taken at both locations and sampled at high resolution (3 mm) intervals for grain size analysis using a Cilas laser particle size analyzer. Downcore chronology was determined through Pb-210, Cs-137 and C-14 dating methods. Using a recent known major storm occurrence at Canton Lake, the signature created by storms in the geologic record was identified. The resulting signature was then used to identify paleostorms in the longer-term record in the Cheyenne Bottoms core. The results were also used to determine storm/climate cycles in the long-term geologic record, and to calculate true return periods for major storms. A better understanding of true return periods and possible increases in frequency or intensity of large storms is essential in the effort to mitigate future damage to infrastructure and loss of human life</p>

<p> Cretaceous Period. There is limited research on organic carbon content of the Pierre Shale in South Dakota. Frequent volcanic eruptions combined with climate change resulted in an increase in carbon dioxide in the atmosphere, leading to decreases in marine oxygen content. Decreasing marine oxygen has been attributed to higher amounts of preserved organic matter in marine sediment. Impact of volcanic ash deposition in the Cretaceous Interior Seaway has not been thoroughly studied. The Pierre Shale also contains the Crow Creek Member, a 5 foot thick layer of unconsolidated sand and rip-up clasts which may indicate a high-energy depositional event. Some hypothesize that it was deposited by a tsunami generated by the Manson impact. Others believe the Crow Creek Member is evidence of a marine low-stand that occurred before the Bearpaw Cyclothem. It is possible that the depositional event that deposited the Crow Creek Member may have led to increases in organic carbon preservation depending on the burial rates and amount of organic carbon preserved. </p><p> To investigate the connection between volcanic ash deposition, the Crow Creek Member deposition, and organic matter preservation of the coastal Cretaceous Interior Seaway, stable isotope geochemistry, trace element geochemistry, and total organic carbon analyses were performed on a 500 foot core drilled near Fort Pierre, South Dakota. Ash beds were identified using X-ray diffraction analysis. Core sampling was driven by location of the Crow Creek Member (above below and within one foot) and by location of ash beds (above below and within one inch), but samples were also taken based on highest and lowest gamma ray values for each five foot (1.52m) core segment. Core sampling was restricted because every other five foot (1.52 meter) section of the Treedam core segement was available for sampling. Statistical T-tests and Z-tests were performed on sample data to determine if there was a significant difference in geochemical signatures between core deposited before and after ash bed deposition and Crow Creek Member deposition. Results and T and Z statistical analyses show no significant changes in stable isotopes nor trace elements as a result of ash bed deposition nor the Crow Creek Member depositional event. Results also indicate that variability of the coastal brackish marine system made any significant trends harder to isolate on such a small scale. Overall &delta;¹³C_org signatures ( -27 to -26 &permil;) indicate that the Cretaceous Interior Seaway was deposited in a brackish shallow marine environment and that there were no drastic changes in sea level throughout the deposition of the Pierre Shale Group that was sampled (Gregory Member up through Virgin Creek Member). The &delta;<p style="font-variant: small-caps">15</p>N data range (-6 to +1 &permil;) show that fixed nitrogen was scarce during the deposition of the Pierre Shale and that most of the available marine nitrogen was likely fixed by cyanobacteria.</p>

No description available.

This project presents an integrated study of the lithostratigraphy and sedimentology of the Haute Normandie chalks (Upper Cenomanian to Santonian), northern France. To enable a detailed lateral correlation across the region a local lithostratigraphic framework is proposed in which the succession is divided up into five basic Formations. Members and marker horizons are also identified. Comprehensive field studies and sedimentary analyses shows the existence of twelve facies. Facies are defined on sediment textures, biogenic composition, resedimented textures, terrigenous content and degree of early cementation. Analysis of spectacular discordant bedding structures, previously interpreted as accretionary "banks", indicates that they are formed from erosion and infill of channels and scours on the sea-floor. Channel and scour structures usually have concave-up basal truncation surfaces with a sedimentary infill of complex fining-upward facies sequences. These structures are compared with erosional furrows, scours and channels of modern continental shelves. The development of channels and scours in the Haute Normandie chalks is attributed to the convergence of oceanic and tidal currents flowing from the proto Atlantic into the epicontinental sea of northwest Europe. A re-examination of shallow seismic refection profiles indicates that the distribution pattern of channels and scours is related to the local influence of tectonic highs within the shallowing chalk sea. Evidence from gravity-flow deposits and turbidites infilling some channel structures may reflect contemporaneous tectonic activity. Dolomitized and dedolomitized chalks occur in the basal horizons of channel and scour structures. Detailed petrographic analysis supplemented with isotope data suggests that dolomitization took place early in the burial history, resulting from a hydrological regime of mixed meteoric and marine ground waters. Late diagenetic dedolomitization is also evident, resulting from the recrystallization of original dolomite crystals within a near surface weathering environment.